Alloy C276 is a nickel-molybdenum-chromium alloy with a small tungsten addition, designated UNS N10276 and Werkstoff 2.4819. It is one of the most widely specified corrosion-resistant materials in the chemical process industries because it performs well in both oxidising and reducing media. The high molybdenum level provides resistance to pitting and crevice attack, chromium supports service in oxidising conditions, and the low carbon and silicon contents keep the alloy weldable.
Corrosion Resistance Benefits
The alloy offers excellent resistance to a broad range of chemical process environments, including:
Strong oxidising agents such as ferric chloride and copper chloride
Reducing media, both organic and inorganic
Wet chlorine, hypochlorite and chlorine dioxide
Formic acid, acetic acid and acetic anhydride
Seawater and saltwater solutions
Flue gas desulfurisation systems, where sulfur compounds and chloride ions are present in most scrubbers
Pipe, plate and other product forms also provide excellent resistance to pitting corrosion and stress corrosion cracking, and the grade is one of the few materials that withstands wet chlorine, hypochlorite and chlorine dioxide. That combination matters in mixed-acid service, where a material suited only to oxidising or only to reducing conditions would fail. The alloy is listed in NACE MR0175 for oil and gas service, which extends its use to sour production and refinery equipment.
Composition and Physical Properties
| Element | Content (%) |
|---|---|
| Nickel | Balance, about 57 min |
| Chromium | 14.5-16.5 |
| Molybdenum | 15.0-17.0 |
| Iron | 4.0-7.0 |
| Tungsten | 3.0-4.5 |
| Cobalt | 2.5 max |
| Manganese | 1.0 max |
| Vanadium | 0.35 max |
| Silicon | 0.08 max |
| Carbon | 0.010 max |
Density is 8.89 g/cm3 and the melting point is about 1370 degC. The high alloy content makes the material considerably stronger than ordinary austenitic stainless steel, which must be taken into account whenever forming loads are calculated.
Mechanical Properties and Fabrication
Tensile strength: 730 MPa minimum, typically about 790 MPa
0.2 % offset yield strength: about 355 MPa
Elongation: 40 % minimum
Hardness: HRB 100 maximum
Hot forming of Alloy C276 is immediately followed by annealing at 1150 degC and water quenching. Cold deformation increases strength, and the alloy work hardens considerably faster than ordinary stainless steel, so intermediate or mid-process annealing is required during extensive cold forming operations. Formability is otherwise similar to that of ordinary austenitic stainless steel, although the higher strength means greater stress is generated during cold working.
Product Forms and Specifications
| Product | Common specification |
|---|---|
| Plate, sheet and strip | ASTM B575 / ASME SB575, ASTM B906 / ASME SB906 |
| Seamless pipe and tube | ASTM B622 / ASME SB622 |
| Welded pipe | ASTM B619 and B626, ASME SB619 and SB626 |
| Bar, rod and wire | ASTM B574 / ASME SB574 |
| Forgings | ASTM B564 / ASME SB564 |
| Fittings | ASTM B366 / ASME SB366 |
| Filler metal | AWS A5.14 ERNiCrMo-4 |
| Coated electrode | AWS A5.11 ENiCrMo-4 |
| European designation | DIN 17750, DIN 17751, DIN 17752, VdTUV 400 |
Available forms include seamless tube, welded tube, pipe, fittings, flanges, plate, sheet, strip, round bar, flat bar, hexagon bar, fasteners, forgings and wire, so a single grade can cover the wetted parts of a complete process line.
Frequently Asked Questions
Q: What are the main benefits of Alloy C276?
Outstanding resistance to oxidising and reducing media, wet chlorine, hypochlorite, seawater and scrubber environments, combined with good formability, weldability and availability.
Q: Is Alloy C276 the same as UNS N10276?
Yes. UNS N10276 and Werkstoff 2.4819 are the standard designations for this nickel-molybdenum-chromium alloy.
Q: Can Alloy C276 be welded?
Yes. Matching ERNiCrMo-4 filler metal and ENiCrMo-4 electrodes are used, and the low carbon and silicon contents limit grain-boundary precipitation in the weld heat-affected zone.
Q: How does it behave during cold forming?
It work hardens faster than austenitic stainless steel, so heavy cold forming requires intermediate annealing; cold deformation itself raises strength.
Q: What is the maximum service temperature?
In oxidising service the alloy is commonly limited to about 675 degC, while higher temperatures are possible in reducing, low-oxygen atmospheres.
Q: Does it meet NACE requirements for oil and gas?
Yes. Alloy C276 is listed in NACE MR0175 and is used for sour service valves, tubing and process equipment within the specified limits.
